This application claims priority to an application entitled xe2x80x9cPHOTODIODE AND METHOD OF MANUFACTURING THE SAME,xe2x80x9d filed with the Korean Intellectual Property Office on Feb. 18, 2002 and assigned Serial No. 2002-8509, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a photodiode which can be used for a light-receiving element and a method of manufacturing the same.
2. Description of the Related Art
Recently, optical communication techniques have been rapidly applied to actual living. Accordingly, high-speed, low-price optical-data-link modules are greatly required.
Photodiodes are a core part of optical-data-link modules, and increasing their modulation rate would result in an increased transmission capacity. A factor of the modulation rate of photodiodes is the capacitance of a chip. In order to increase the modulation rate of photodiodes, the capacitance of the chip must be decreased. In order to decrease the capacitance, the area of the active region must be reduced. However, the light-receiving area will be reduced in proportion to the reduction of the area of the active region. If the light-receiving area is reduced, the photoelectric transformation efficiency will be lowered. The coupling effect with an optical fiber also will be lowered during a packaging process. As a result, the degree of freedom of subsequent processes will be lowered resulting in various problems. Therefore, there is a need to improve the light-receiving efficiency and the coupling effect with an optical fiber, while decreasing the capacitance of the chip.
FIGS. 1 and 2 are sectional views showing the structures of conventional photodiodes.
In the photodiode as shown in FIG. 1, an active region 9 having a planar structure generates a light-induced current. A buffering layer 2, a light absorbing layer 3, and an epitaxial layer 4 are formed in sequence on a substrate 1 by metallo-organic chemical-vapor deposition. A SiNx layer 5 is then deposited on the epitaxial layer 4 and patterned to be used as a diffusion mask for depositing a diffusion source on a position where the active region will be formed. A diffusion process is then performed to form a plane surface junction. Subsequently, a SiO2 layer 6, a p-type electrode 7, and an n-type electrode 10 are formed.
In the prior art explained above, the active region 9 generating a light-induced current has a planar structure. In practical use, a front side illumination, which irradiates light at the surface on which a diffusion process has been performed, is used to irradiate light to the active region. Therefore, the area of the active region is identical to that of the light-receiving part. If the area of the active region is reduced to increase the modulation rate of the photodiode, the light-receiving area also will be reduced. Consequently, the photoelectric transformation efficiency and the coupling effect with an optical fiber also will be lowered causing such problems as lowering of the degree of freedom in subsequent processes.
In the photodiode as shown in FIG. 2, a micro-lens 8 is formed on a surface of the substrate 1 opposite the surface on which the active region 9 is formed. The purpose is to utilize the back-side illumination for the incidence of light to the active region 9.
However, in the prior art mentioned above, the rear side of the substrate must be processed after grinding a wafer to have the same thickness as a final chip. Therefore, the pattern between the front and rear sides of the chip must be aligned precisely.
The present invention provides a light-receiving diode, which can increase the light-receiving area and improve the light-receiving efficiency, while decreasing the capacitance, and to provide a method for manufacturing the light-receiving diode.
One aspect of the present invention is to provide a light-receiving diode, which can improve the light-receiving efficiency without performing a process on the rear side of a thin wafer or a pattern-alignment process between the front and rear sides of the wafer.
According to one embodiment of the present invention, a photodiode includes: a substrate; a buffer layer and a light-absorbing layer laminated in sequence on the substrate; an epitaxial layer formed on the upper surface of the light-absorbing layer, having an active region with a surface in a convex-lens shape; a dielectric layer formed on the upper surface of the epitaxial layer; a first metal electrode formed on the upper surface of the dielectric layer; and a second metal electrode formed on the under surface of the substrate.
According to another embodiment of the present invention, a method for manufacturing a photodiode is provided and includes the steps of: forming a buffer layer, a light-absorbing layer, and an epitaxial layer in sequence on a substrate; selectively etching said epitaxial layer of an active region to form a surface in a convex-lens shape; forming a dielectric layer on the upper surface of the epitaxial layer excluding the active region; performing a diffusion process using the dielectric layer as a diffusion mask to form a diffusion layer on the active region in the convex-lens shape; forming a first metal electrode on the top of one side of the dielectric layer; and, forming a second metal electrode on the under surface of the substrate.
In the embodiment, the step of selectively etching the epitaxial layer of an active region to form a surface in a convex lens shape is achieved by: applying a photosensitive film on the upper surface of the epitaxial layer, and forming a photosensitive mask pattern on the upper surface of the epitaxial layer excluding the active region by an exposure and development process; and, wet-etching the epitaxial layer in a lens-forming etching solution.